Keywords inhalation exposure;oropharyngeal aspiration;ozone;lipopolysaccharide;hyperoxia;vanadium pentoxide;bleomycin, pulmonary function;ovalbumin, cigarette smoke. The Respiratory Toxicology Group (RTOX) conducts studies of chemicals for which inhalation is the primary route of human exposure. Inhalation studies are conducted at the NIEHS inhalation facility through an in-house research contract. Research efforts are directed toward understanding the biochemical and molecular mechanisms of toxicity of inhaled chemicals. Studies are designed and conducted to provide support to the National Toxicology Program (NTP) and the Division of Intramural Research (DIR). Research activities provide support for NTP-sponsored inhalation studies by conducting special studies on inhalation dosimetry and mechanisms of toxicity, and by providing a quick response capability for studies requiring inhalation exposure. Recent work includes studies of bronchiolitis obliterans caused by inhalation of artificial butter flavoring components, mechanisms of pleural fibrosis caused of indium phosphide particulate, brain lesions caused by inhaled carbonyl sulfide. The RTOX group supports DIR scientists by providing expertise and capability for conducting inhalation exposures and pulmonary function measurements. RTOX activities include the development of inhalation exposure technology, and models for investigating pulmonary disease. Current RTOX support for DIR investigators includes providing animal care and maintenance for genetically-modified mice, inhalation exposures to ozone, hyperoxia, endotoxin, cigarette smoke and ovalbumin. Additional support is provided for oropharyngeal aspiration studies and in measurement of pulmonary function changes.